Low molecular weight polycarboxylic acid polymers and their salts are useful as dispersants, scale inhibitors, detergent additives, sequestrants, etc. Generally a weight average molecular weight below 50 000 is necessary for effective performance and often weight average molecular weights below 10 000 are most effective. It is common to use chain transfer agents in the polymerization reaction to produce low molecular weight polymers. Hypophosphorous acid or its salts (e.g. sodium hypophosphite) are a special type of chain transfer agent, chosen to introduce phosphorus-containing groups, like phosphinate and/or phosphonate groups into water soluble polymers to modify their performance properties. In many cases, however, the overall performance properties of the resulting polymer compositions still need improvement.
Thus, there continues to be a need for polymer compositions which have a very low molecular weight, preferably in conjunction with a high solids content. Such compositions are suitable as dispersants, sequestrants, etc. They are especially suitable for producing detergent compositions that can be employed in laundry washing.
U.S. Pat. No. 5,409,571 describes the use of terpolymers with maleic acid units, acrylic acid units and hypophosphorous acid units as scale deposition inhibitors for Kraft digesters.
EP 0877076 A2 describes detergent formulations comprising at least one water soluble polymer or salt thereof bearing at least one phosphonate group. The polymers used in the formulations, may comprise monoethylenically unsaturated (C3-C7)-mono-carboxylic acids, such as acrylic acid and methacrylic acid, and monoethylenically unsaturated (C4-C8)-di-carboxylic acids, such as maleic acid and itaconic acid. With regard to suitable methods to prepare the phosphonate containing polymers reference is made to U.S. Pat. No. 4,046707, U.S. Pat. No. 5,376,731, U.S. Pat. No. 5,077,361 and U.S. Pat. No. 5,294,686.